A dead whale six to eight metres long has washed up on Papamoa Beach in Bay of Plenty.

The carcass floated into shore late this afternoon after being spotted floating in Tauranga Harbour over the weekend, Department of Conservation officer Jeff Milham said.

It was believed to be a juvenile sperm whale and had been dead for a while.

If it was confirmed as a sperm whale, iwi would take the jaw bone and the rest of the whale would be buried, Milham said.Police were called to the beach after witnesses mistook the whale for a capsized yacht, SunLive reported.

Papamoa Surf Lifeguards Matt Strange, 19, and Hamish Smith, 18, went out in an IRB after spotting the whale from shore.

"There was a small black patch of skin and all of the rest was white," says Matt.

They managed to get within 50 metres of the whale when they began to smell it.